The objective of this proposal is to better define the ability of ultraviolet B radiation to modulate cutaneous cell-mediated immune responses. Contact hypersensitivity will be used as the prototype immunologic response. Previous observations in mice have shown that relatively low doses of UVB radiation in vivo followed by the epicutaneous application of hapten are capable of inducing antigen-specific unresponsiveness. The studies in this proposal aim to utilize a murine model to examine the action spectrum for this effect and to define the range of contact sensitizers susceptible to the induction of unresponsiveness by UVB. Efforts will be made to determine the duration of the unresponsiveness and to define the ability of suppressor T lymphocytes to inhibit certain in vitro correlates of the contact hypersensitivity response. Attempts will then be undertaken to extend the observations in the murine system to human subjects. These studies will establish whether antigen presentation to T lymphocytes by the skin is impaired following exposure to UVB doses similar to those to which humans are exposed during recreational activities. It is hoped that these studies may lead to important new knowledge regarding the ability of UVB exposure to modulate immune responses in the skin.